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Stellar Disappearing Act Unravelled

The paper 'Towards the field binary population: influence of orbital decay on close binaries' (Astronomy & Astrophysics 543, 2012, A126) co-authored by Christina Korntreff, PhD student in the Computational Science division of JSC, was recently highlighted in Nature online news. The article reports on the unexpected finding that many stars may have been born as two separate stars - a binary system, which merged into a single system during the first million years of their life. The original article by Korntreff et al. describes the development of binary populations from their initial state within a stellar cluster to their final state in the stellar field.

Most stars form in clusters, where two important dynamical processes influence the binary population: i) gas-induced orbital decay of embedded binary systems and ii) destruction of soft (wide) binaries in three-body interactions. The paper focuses on the process of orbital decay, which has been largely neglected so far.

Using a combination of analytical calculations and dynamical N-body modelling, the authors show that as the cluster evolves, short-period binaries are merged to single stars by the gas-induced orbital decay, while the dynamical evolution in the cluster destroys long-period binaries. The combination of these two equally important processes explains how the binary population in a cluster environment evolves into the binary population observed.